The invention is related to power supplies for deployable Microsystems such as TeraHertz sensors, bioengineering nanodevices, micro-robots, nanofabrication and planar antennas. Supplying electrical power to micro-devices from a battery or from wires is often impractical because the weight of the wires or battery may impair the performance of the microdevice being powered. The present invention provides electrical power from electromagnetic radiation incident on a local antenna mounted on the microdevice to be powered. One problem with such an arrangement is that the antenna performance is affected by the electrical characteristics of the microdevice on which it is mounted. Thus, the design of the underlying microdevice is constrained so as to avoid detracting greatly from antenna performance, which is inconvenient. Another problem is that an antenna sufficiently small to fit on a microdevice, such as a micro-miniature dipole antenna, will typically have poor gain in the direction of the radiation because such an antenna will have little directionality. A further problem is that a diode must be employed to rectify the received RF power. The impedance of the diode will not necessarily match the impedance of the antenna, depending upon the frequency of the incident radiation, so that some power will be lost. Yet another problem is to find a radiation frequency at which the ideal antenna size is small compared to the microdevice on which it is to be mounted, but not so small that the frequency reaches the optical range in which a diode rather than an antenna must be used. This would sacrifice the advantage of tunability of an antenna. Further, it would be desirable if the radiation frequency were one that readily penetrated certain materials such as plastic, human skin (for bio-engineering applications) and the like.
The invention is embodied in a monolithic semiconductor integrated circuit in which is formed an antenna, such as a slot dipole antenna, connected across a rectifying diode. In the preferred embodiment, the antenna is tuned to received an electromagnetic wave of about 2500 GHz so that the device is on the order of a wavelength in size, or about 200 microns across and 30 microns thick. This size is ideal for mounting on a microdevice such as a microrobot for example. The antenna is endowed with high gain in the direction of the incident radiation by providing a quarter-wavelength (30 microns) thick resonant cavity below the antenna, the cavity being formed as part of the monolithic integrated circuit. Preferably, the integrated circuit consists of a thin silicon membrane overlying the resonant cavity and supporting an epitaxial Gallium Arsenide semiconductor layer. The rectifying diode is a Schottky diode formed in the GaAs semiconductor layer and having an area that is a very small fraction of the wavelength of the 2500 GHz incident radiation. Preferably, the antenna is a pair of half-wavelength dipole slots in the overlying conductor layer that forms respective power output terminals and respective tuning capacitors across the rectifying diode. At the 2500 GHz frequency, the pair of half-wavelength dipoles exhibit an impedance that nearly matches the impedance of the Schottky rectifying diode, a significant advantage. A most significant advantage is provided by the combination in the integrated circuit of the antenna with the quarter wavelength resonant cavity, because the antenna behavior is determined principally by the resonant cavity. The resonant cavity both provides the directional gain of the antenna and isolates the antenna from surrounding structure. In this way, the integrated circuit may be mounted on any structure without appreciably affecting the antenna behavior.